1. Field of the Invention
The present invention relates to the field of marine survey data acquisition and processing methods. More specifically, the invention relates to methods for attenuating strong marine seismic noise.
2. Discussion of Related Art
To achieve high density surveys in regions having a combination of imaging and logistical challenges, a high trace density and closely spaced streamers may be used, however, this presents the potential of entangling and damaging streamer cables and associated equipment, unless streamer steering devices are closely monitored and controlled. Wide-azimuth towed streamer survey data is typically acquired using multiple vessels, for example: one streamer vessel and two source vessels; two streamer vessels and two source vessels; or one streamer vessel and three source vessels. Many possible marine seismic spreads comprising streamers, streamer vessels, and source vessels may be envisioned for obtaining wide- or rich-azimuth survey data. Assignee's U.S. Pat. No. 7,400,552 , discusses some of these. This patent discusses shooting and acquiring marine seismic data during turns of linear marine surveys and during curvilinear paths. A great leap in acquisition technology was described in another assignee's co-pending application Ser. No. 12/121,324, filed on May 15, 2008 , which describes methods for efficiently acquiring wide-azimuth towed streamer seismic data, which is also known as the “coil shooting” technique. These non-linear survey methods deviate greatly from the traditional straight line surveys and frequently encounter a lot more noises from various sources, such as ocean current, towing mechanism, steering devices.
Regardless the acquisition methods used in seismic survey, the noise attenuation is always a major issue during data processing. There are many methods to attenuate noises. The methods could be classified into three categories:                methods to discriminate the noise from the signal based on apparent velocities;        methods to discriminate the noise from the signal based on amplitudes; or        methods that adaptively estimate the noises based on noise coherency.        
Seismic data acquired in the presence of marine currents could be affected by very strong noise that could contaminate a large number of traces. When the noise energy is comparable to the signal energy, then the noise is referred to as strong noise; when the noise energy is greater than the signal energy, then the noise is very strong noise. The existent noise attenuation methods applied on such data do not perform well and the results typically have large amount of noise left and the signal amplitudes are not accurately preserved.
One way to handle these cases is to apply a combination of different methods that requires sorting the data in different domains, like common receiver domain or common offset domain and this could make the processing quite expensive.
While the Q suite of advanced technologies for marine seismic data acquisition and processing may provide detailed images desired for many reservoir management decisions, it is desirable to have methods that can improve the data quality and reduce the processing costs.
References:    [1]. Peter W. Cary, Changjun Zhang, “Ground roll attenuation with adaptive eigenimage filtering”, SEG 2009, Houston, Tex.